It is widely known to monitor the output beam from a laser system to measure various output beam parameters, such as power level, pulse amplitude, pulse width, spatial mode, etc. during laser system operation. Typically, a beam splitter is used to pick off a small portion of the output beam and direct it to one or more detectors.
Different types of detectors are used to measure the different laser beam parameters. Therefore, a single laser system may contain several different types of detectors. Each detector type accurately operates with a particular range of optical input powers. If the power of the reflected beam impinging upon a detector is below that detector's operational range, the measurement will be inaccurate. If the incoming power is above the detector's operational range, the detector can become saturated, such that the measurement will be inaccurate. In more severe cases, the detector could be damaged.
It is known to place neutral density filters in front of detectors to attenuate the intensity of a beam impinging upon the detector. It is also known to move and/or expand the operational range of detectors by designing special detector electronic circuits that automatically adjust the gain of the detector circuit to compensate for different power levels.
Modern laser systems produce output beams having widely varying power levels, pulse widths, and wavelengths. These systems require different detector types to measure the different laser beam parameters, such as average power, pulse energy, pulse width, pulse shape, spatial mode, etc. The various types of detectors used with these lasers must operate over the flail range of operational output powers, pulse widths, and wavelengths.
Using neutral density filters in front of detectors in modem laser systems have several drawbacks. First, for systems with a plurality of detectors, adding these additional optical elements for each detector adds to the complexity and cost of such a system. Second, even though these filters are labeled "neutral density", they are not fully wavelength independent. Therefore, if the output beam is tuned to a different wavelength, the attenuation of the neutral density filter can change. Finally, a neutral density filter cannot maintain proper input power to the detector if the laser power is changed dramatically.
Complex and costly electrical systems have been incorporated into detector devices to change the gain of the detector system to compensate for changes in power level. The changed gain enhances the effective operational range of the detector, allowing it to measure a wider range of power levels. However, these electrical systems are costly for those laser systems containing many detectors. Further, these electrical circuits can only broaden the detector's operational range only so far. Electronic circuits cannot compensate for extremely large changes in input power, pulse width, or wavelength. Nor can they prevent damage to the detector from very high input beam powers.
There is a need for a simplified means for monitoring the different parameters of the output laser beam that is substantially wavelength insensitive. Further, there is a need for a means for monitoring the different parameters of the output laser beam despite very large changes in output power, pulse energy, pulse width, and wavelength.